Negative working flexographic printing plates typically comprise a base and a photopolymer layer which is cured by image-wise exposure to (UV) light. During a subsequent processing step, the unexposed areas are removed by a developing liquid and a relief plate is obtained wherein the printing areas are raised above the surrounding non-printing areas. In positive working plates the reverse occurs. The relief image distinguishes flexography from other printing techniques such as lithography (planographic process wherein printing and non-printing areas are part of the same surface) and gravure (printing areas are recessed below the level of the non-printing areas).
Image-wise exposure of a flexographic plate is generally obtained by flood exposure of the photopolymer layer through a contact mask which is typically a film negative that is transparent in printing areas and opaque in the non-printing areas.
This film negative is a reproduction of an original in the form of multiple screened dots and lines composed of developed silver, originating from an exposed and developed classical photographic material, such as a camera, recording or contact photographic material. However, these conventional photographic materials, which are based on silver halide chemistry, are complex materials, which are rather costly and demand a sophisticated technology to manufacture them. Moreover, they require wet processing steps involving several chemical solutions which is a drawback from an ecological point of view.